The present invention relates to a process and a device for electrolytic depositon of a metal coating containing solid particles held in suspension, hereinafter called suspension electrolyte. The device required to carry out this process features a container to hold this suspension electrolyte and an anode, the workpiece to be heated being made the cathode.
The use of metals in the technical field frequently calls for an improvement in surface properties, in particular wear resistance, hardness and sliding properties and general wear resistance characteristics. Numerous applications for aluminum in automobile and machine manufacture in particular are possible only in combination with hard, wear-resistant coatings. Electrolytic deposition of a metal layer incorporating hard particles of material represents a simple and, for many wear problems, suitable possibility for improving the surface.
The dispersion coatings, in many cases the nickel/silicon carbide system is usefully employed, which result from simultaneous deposition of metal and solid particles from a suspension electrolyte exhibit many and varied properties by appropriate choice of matrix material, particle material, size and distribution.
Electrolytically deposited dispersion coatings have been known already for some decades. Equipment used to produce them are described e.g. in the journal "Schmiertechnik", 11 (1980), pp 81-86. In an earlier article in the journal "Oberflachentechnik" (1975), pp 45-52 attention is drawn to the fact that movement of the bath i.e. the electrolyte is of very great importance for the rate of incorporating the solid particles in the metal as it is deposited.
There it is suggested that the movement of the bath be achieved by injection of air, circulating the electrolyte, or with the help of stirrer. The effect of the movement of the bath is intended to insure that the solid particles along with the electrolyte reach a place above the workpiece so that the said particles can settle on the surface of the workpiece under the force of gravity and be bonded there by the metal coating.
Moving the bath by means of conventional stirrers or circulating it is not suitable as changes in the turbulence along the surface of the part to be coated results in non-uniform incorporation of solid particles into the metal of the coating. Although better results have been obtained with air injection than with the other above mentioned measures, this method is also not suitable inasmuch as it leads to inhomogeneities or differences in concentration in the suspension electrolyte, and thus also results in irregular incorporation of the dispersion in the coating.
The object of the present invention is to eliminate these disvantages.